CA2361983A1 - A sanitary napkin having regions of improved flexibility - Google Patents

Abstract

The invention provides a sanitary napkin having a fibrous, liquid permeable body facing cover layer, and an absorbent system. The sanitary napkin has a thickness of less than or equal to 5 mm. The sanitary napkin is composed of to regions each having substantially uniform composition yet one region having stiffness that is less than 90% of the stiffness of the other.

Description

A SANITARY NAPKIN HAYING REGIONS OF IMPROVED FLEXIBI>rITY
Field of the Invention The present inventyon relatos genorally to sanitary absorbent articles and in partlcul~rr to such artides, for example sanitary napkins, which are thin, highly absorbent, and yet reasonably flexible.
~ackaround of the Invention io Sanitary absorbent articles find wide and variod use in absorbing and trapping body fluids and maintaining body surtaces in a state of dryness and comfort.
The development of materiols having a high liquid absorption capacity per unit voiunre has allowed the required overall thickness of sanitary absorbent articles to be reduced providing products which are I~ss obtrusive to wear. Such articles find .
use, for example in feminine protection devices such as sanitary absorbent napkins.
Thin sanitary n~pkins are generally constructed of rr~ultipl~ layers of m~terial each having a particular function, as for exmmple disclosed In U_S. Patent Number 5,375.788 to T.W. Osborne III. The sanitary napkin dibclosed In this document 2o includes a top sheet which is placed nearest the body surface of the wearer, an acquisition or transfer sheet with a relatively open structure having a relatively high void volume for accepting fluid and transporting fluid tv an absorbent core which serves as thp main disposaitory for liquid absorbed by the napkin. The napkin also has a barrier sheet which is impervious to liquid absorbed Into the absorbent core is and serves as a proteetlve barrier betweon the absorbent core material and the wearer's clothing. The absorbent core has a high liquid absorption capacity relative to the top and transfer sheets and can be made from materials such as wood pulp, creped aetlulose wadding, absorbent foarrrs and sponges, polym~ric fibres and polymeric gelling agents. The thickness of the napkin disclosed in U.S. Patent 3o Number 5,575,786 is preferahly less than 2.5 mm.
PPC-763 ~c~r ._ A problem which confronts designers of sanitary absorbent napkins is their ability to retain the absorbed liquid when subjected to mechanical loads as would be applied by the wearer in uae. When subjected tn such loading, liquid can leak from the absorbent core and rewet the layers above through which liquid was s originally passed to the absorbent sore- As the transfer and cover layers are made from materials with little absorption capacity, the liquid expelled from the absorbent core will tend to reside next to the body surface of the wear~r resulting in discomfort and possible staining of the wearers garments. Typically in the prior art, this problem was addressed by utilizing materials of construction of the thin sanitary absorbent is article, which Improved its ability to r~tain liquids under load.
However, the material which provides adequate capacity In addressing this absorbency issue, is frequently too stiff for the users comfort. The prosent Invention attains improved usor comfort by physically modifying one or more rogions is of a relatively stiff absorbent core to thereby improve flexibility In strategic ar~as of the napkin.
According to the present invention there is provided a sanitary napkin adapted to he worn in the crotch portion of an undergarment, the napkin having a ~u thickness of less than about 5 mm and comprising a central absorbent zone, the central absorbent zone comprising a fluid-permeable, body-facing cover layer:
a fluid impermeable, garment facing barrier layer and an absorbent system. The centre) absorbents Zone has a minimum width of 45 mm and is formed from a substantially uniform composition of absorbent materials. The central absorbent zone further Z s comprises a first region and a second region adjacent said first region, said llrst region having a stiffness, and said s~cond region having a stiffness that is less than 90°~ of the stiffness of the first region-;i U
PPG-7fi3 BRIEF DESCRIPTION OF THE DRAWING
Examples of embodiments of the present invention will now be described with reference to the drawings, in which:
Figure 1 is a top elevational view of a sanitary napkin in aooordance with an embodiment of the present invention, the cover layer of the sanitary napkin being partly removed to Show the absorbent system:
io Figure 2 is a perspective view of the sanitary napkin of Figure 1, depicted in a posiiivn attained when the sanitary napkin is placed in the undergarment of a wearer;
Figure 3 is a bottom plan view of tha sanitary napkin shown in Figure 1;
Figure 4 is a cross-sectional view taken along tho longitudinal centerline of the sanitary napkin shown in Figure 3;
Figure 5 is a schematic illustration of means for air-laying absorbent lu material for making an example of an absorbent core of the sanitary napkin according to an embodiment of the present invention, using flour air-laying heads fvllowod by means for compacting the air-layered matenal;
Figures 6a and 6b show throe and four layer embodiments respeCtlvely 2s of an absorbent core that can be used in the sanitary napkin of an embodiment of invention; , .
Figure 7a shows a top view of an embodiment of the invention in which the adhesive IayQr is discontinued in the region of the cuts in the absorbent region;
:i U

Q -Figure 7b dcpic.-is a cross sPCtional view of the sanitary napkin shown in Figure 7a; and Figures a -11 each shows an alternative embodiment of the sanitary napkin of the present invention.
DESCRIPTION OF TH~EF~n EMI30DIMENTS
Referring to Figures 1 and 2, there is shown an embodiment of the zo prosent Invention, a feminine sanitary napkin 20.
The sanitary napkin 20 has a main body 22 with a first transverse side 26 defining a front portion thereof and a second transverse sid~ 28 defining a rear portion thereof and deTining thorQbetween a length. Each of these sidos is preferably drcuate. The mam body also has two longitudinal sides, namely a longitudinal side 30 and a longitudinal side 32. The main body has a width defined by th~ distance between lonpiludinal side 30 and longitudinal side 32. The sanitary napkin ZU has a thickness not exceeding about 5 mm. Pr~ferably, the thickness is less than 3.5 mm, more pr~f~rably less than 3 mrT~, and most preferably, it is of about Zo 2.8 mm.
The sanitary napkin 20 has a longitudinal centerline 34 that is an imaginary line bisQCting the sanitary napkin 20 In twc~ substantially identice~) halves.
The main body 77 also has an imagin~ry transverse line 3es perpendicular to th~
zs longitudinal centetllne 34.
Projecting laterally outward from each of the longitudinal sides 30, 32 Is a flap 38, 40 (respectively). Th~ flaps 38, 40 are in the shape of an isosceles trapezoid with the top adjoining the longitudinal side and the base at the distal end.

S
As depicted in Figure 4, the main body 22 is of a laminate construction drrd preferably comprises a fibrous fluid-permeable body facing cover layer etZ, an absorbent system 44, and a fluid-impervious barrier layer 50. The absorbent system rraty be formed from a single layer of absorbent materiel or alternatively may be formed as s laminate of two or more layers of absorbent material. In a preferred embodim~nt, the absorbent system comprises two component layers, namely a first absorbent layer 46 (vommonly known as "transfer layer") and a second absorb~nt layer 48 (commonly known as "absorbent core'). Alternatively, a single layer, namely the second absorbent layer 48, can form the absorbent system 44. Each of ~ o these layers is described in hereinbelow.
_MY-Cover Lever The cover layer 42 may be formed from any flexible, liquid permeable is materiel that is non-irritating to a user. Suitable liquid permeable materials include, but are not limited to woven fabrics, non-woven fabrics, aperturad plastic films, and the like. Tho cover layer 42 is preferably a relatively low density, bulky, high-loft non-wvven web material. The cover layer 42 may be composed of only one type of fiber, such as polyester or polypropylene or it may be composed of bi-component yr 2o conjugate fibers having a low melting point component and a high melting point component. The fibers may tie selected from a variRty of natural and synthetic materials such as nylon, polyester, rayon (in cortrbination with other fibers), cotton, acrylic fiber and the like and combinations thereof. An example is the non-woven cover layer of sanitary napkins sold by Johnson 8~ Johnson Ins. of Montreal, Canada under the trademark Stayfree Ultra-Thin Cottony Dry Cov~r.
Bi-component fibers may be rnade up of a polyester layer and a polyethylene sheath. The use of appropriate bi-compondnt materials results m a fusible non-woven fabric. Exampl~s of such fusible fabrics ere described in U.S.
so Patent 4,555,446 issued November 50, ~ g85 to Mays. Using a fusible fabric PPC-?63 incraase5 the ease with which thc~ cover layer may be mount~d to the adjacent first absorbent Isyer and/or to the barrier layer.
Th~ cover layer 42 preferably has a relatively high degree of wettability, although the individual fibers comprising the cover may not be particularly hydrophilic. The cover material should also contain a great number of relatively large pores. This is because the cover layer 42 is intended to toke-up body fluid rapidly and transport it away frortr the body and the paint of deposition.
Advantageously, the fibers which make up the cover layer 42 should not lose their physical propirrtios io when thQy are w~ett~d, in other words they should not collapse or lose their resiliency when subjected to water or body fluid. The cover layer 42 may be treated to allow fluid tv pass through it readily. The cover lay~r 42 also functions to transfer the fluid quickly to the ether layers of the absorbent sy$tem 44. Thus, the cover layor 42 is advantageously~wottable, hydrophilic and porous. When romposed vt synth~tic 15 hynrophobic fibers such as polyester or bi-component fibers, the cover layer 4? may be treated with a surtactant tv impart th~ desired degree of wettability. An alternative embodiment would be that the cover layer 42 is composed of an apertured film.
The cover layer 42 may be affixed, e.g., by embossing to the remainder 20 of the absorbent system 44 by affixing the cover to the underlying layer In order to assist fluid transport tram the cover tv the absorbent system. Such affixation may be effected locally, at a plurality of sites or ovQr the entire coat~ct surface of the cover layer 42 absorbent system 44. Exemplary means of affixing the covQr layer to the absorbent system 44 are adhesion and fusion.
Main Body - Absorbent Svstom -!=ir~st Absorbent Loyer Adjacent to the cover layer 42 on its inner side and bonded to the cover layer 42 is a first absorbent layer 46 that forms part of thee absorbent system 44. The so first absorbent layer 46 provides the means of receiving body fluid from the cover layer 41 and holding it until an underlying second absorbent layer has an opportunity to absorb the fluid, and therefore acts as a fluid transfer or acquisition layer.
The first absorbar~t layer 46 is. preferably, mare dense than and has a s larger proportion of smaller pores than the cover layer 42. These attributes allow the first absorbent layer 46 to contain body fluid and hold it away from the outer side of the cover layer 42, thereby preventing the fluid from re-wetting the cover layer 42 and its surface. However, the first absorbent layer 46 is, preferably, not so dense as tv prevent the passage of the fluid through the layer 46 into the underlying second io absorbent layer 48.
The first absorb~nt layer 46 may be composed of fibrous materials, such as wood pulp, polyester, rayon, or the like, or combinations thereof.
Alternatively, the first absorbent layer 46 may bP composed of non-fibrous materials is such as flexible foam. In a preferred embodiment, the first absorbent layer 46 is composed of fibrous materials and may include thermoplastic fibar5 for the purppse of stabilizing the layer and maintaining its structure) integrity. The first absorbent layer 48 rtray be treated with surtaetant on one or both sides in order to increese its wettability, although generally the first absorbent layer 46 is relatively hydrophilic and ao may not require treatment. The first absorbent idyer 46 is preferably bonded on both sides to the adjac~nt layers, i.e. the cover layer 42 end an underlying second absorbent layer 48.
Materials particularly suitable for use in the first absorbent layer 46 ~5 have a density in the range of about 0.04 to 0.05 g/cc. a basis weight in the range from about 80 to 110 g/m~ and a thickness in the rangy of about 2 to 3 mm and in paNcular a thickness of 2.6 mm. Examples of suitable materials for the fist absorbent layer are through air bonded pulp sold by Buckeye of Memphis, Tennessee, under the designation VIZORB 3fIQ8, which has a basis weight of 110 so g/ma and VIZORB 3010, which has a basis weight of 90 g/m2 Main Bodv - Absorbfnt Systom-Second Absorbent Layer Immediately adjacent to and bonded to the first absorbent Isyer 46 is the second absorbent layer 48.
As noted above, the absorbent system preferably comprises both the first and second absorbent layers. In one embodiment, the first absorbent layer 46 has a width that is at least about the same as th~ width of the second absorbent zo Isyer 48. in anottrer embodiment, the first absorbent layer 46 has a width that exceeds the width of the second absorbent layer 48. In either of these embodiments, the "width" of the absorbent sybtc~m is defined to be the smaller of th~
widths of the first and sQCOnd absorbent layers end it rofers to the maximum measurerrmnt dcross that layer along a line perpendicular to the longitudinal is centerline.
In an alternative embodiment, the absorbent system 44 is formed of a single layer, thp second absorbent layer 48. In this embodiment the width of the absorbent system is defined to be the width of the second absorbent layer 48.
In the preferred em6cxiiment, the width of the absorbent system exceeds 45 mm. In an alternative embodiment the rrrinimum width of the absorbent system is 64 mm.
zs In one embodiment, the second absorbent lay~r 48 is a blend or mixture of oeilulosic fibers and superabsorbent disposRd in and amongst frbers of that pulp.
In a specific eacample, the second absorbent Isyer 48 is a material so containing from about 40 weight percent to about 95 weight percent cellulosic fibers g _ and, more specifically from about 60 to about a0 weight percent cellulosic ~bRrs.
Such a material may contain from about 5 weight percent to about 60 weight percent SAP (superabsorbent polymers), prefmrably form about 20 to about 55 weight SAP.
and even more preferably from about 30 tc~ 45 weight percent SAP, and most ;, preforably about 40 weight percent SAP. The material has a water content of less than about 10 weight percent. As used herein, the phrase "lweight percent"
means weight of substance per weight of final material. 8y way of example, 10 weight percent SAP means 10 glm2 SAP per 100g1m1 basis weight of the material.
io Cellulosic fibars that can be used in the second absorbent layer 48 are wQll known in the art and include wood pulp, cotton, ?fax and peat moss. Wood pulp is preferred. Pulps can be obtained from mechanical or chemi-mechanical, sulfite, kraft, pulping reject materials, organic solvent pulps, etc. Both softwood and hardwood species ;aye useful. Softwood pulps are preferred. It is not necessary to m treat cellulosic fibers with chemical debondlng agents, cross-linking agents and the like for us~ in the present material.
The second absorbent layer 48 can contain any superabsorbent polymer (SAP), which SAPS are well known in the art. For the purposes of the ao present invention, the term "supeirabsorbent polymer" (car "SAP°) refers tv materials which are capable of absorbing and retaining at least about 10 times their weight in body f~mds under a 0.5 psi pressure. The superabsorbenl polymer particles of the invention may be inorganic or organic cro~slinked hydrophilic polymers. such as polyvinyl alcohvls. polyethylene oxides, crosslinkvd starches, guar gum, xanthan 4J gum, and the like. The particles may be In the fic~rm of a powder, grains, granules, or fibers. Pref~rred superebsorbent polymer particles for use in the pros~nt invention are crossllnked polyacrylates, such as the product offered by Surnltomo Seika Chemicals Go_, Ltd. Of Osaka, Japan, under the designation of SA80N Type II".
the product offered by Stockhausen, Inc_ of Greensboro, North Carolina, under the designation of 7440, dnd the product offered by G"hemdal International, Ine.
of Palatine, Illinois, under the designation of 2100Ai.
The second absorbent layer 48 can be manufactured by using air-laying means. in accordance with Figure 5, cellulosic fibers (e.g., pulp) are processed using a hammer mill to individualise the fibers. The individualized fibers are blended with SAP granules in a blending systptn 9 and pneumatically conveyed into a series of forming heads 2. The blending and distribution of fibers and SAP
granules ran be controlled seporately for each forming head. Cvntrvlled air in circulation and winged agitators it ~ach chamber produce uniform mixturd and distt~ibuGvn of pulp and SAP. The SAP can be thoroughly and homogeneously blended throughout the material or contained only in specific strata by distributing it to selected forming heads. ~iber$ (and SAP) from each forming chamber are deposited by vacuum onto a forming wire 3 thus forming a layered absorbent web.
15 The web Is subseqnentiy comer~ssad using calendars 4 to achieve desirable density. The densified web is wound into a roll 5 using conventional winding equipment. The forming wire 3 can be covered with tissue paper to reduce the loss of material. The tissue paper Isyer can be removed prior to calendering or incorporated into the formed material. In a possible variant, the first absorbent layer zo 48 can be formed integrally with the second absorbent layer 48 to provide a unitized absorbent system 44. This can be achieved by providing the apparatus depicted in Figure 5 with an additional forming head (not shown in the drawings) to deposit on the second absorbent layer 48, by air laying and prier to calendering, a layer of material to form tha first absorbent layer 46.
The second absorbent layer 48 of the present invention is of high density and in a specific example has a density of greater than about 0.26 glee.
Spwcifically, the second absorbent layer 48 may have a density in the range of from about 0.25 glee to about 0.60 glee. More specifically, the density Is from about 0.25 IZ
glee l~ about 0.40 g/cc and, even more specifically from about 0.h glee to about 0.35 glee.
Air-laid absorbents are typically produoed with a tow density. To s achieve higher density levels, such as the examples of the second absorbent layer 48 given above, the air-laid material is compar:tRd using calendars as shown in Figure 5. Compaction is accomplished using means well known In the art.
Typically such compaction is carried out at a temperaturE of about 100 degrees C and a load of about 130 Newtons per millimeter. The upper compaction roll is typically made of i o steel while the lower compaction roll is a flexroll having a hardness of about 85 SH
D. It Is preferred that both the upper ~rnd lower compaction rolls be smooth, although lhc~ upper roll can be engraved.
The secand absorbent layer 48 can be prepared ever a wide range of is basis weights. The second absorbent layer48 can have a basis weight in the range of from about 100 B/m~to about 700 g/m2. In a specifrc Qxa'nple, the basis weight ranges from about 150 g/m~ to about 400 g/ma. Preferably the basis weight ranges from about 200 g/m2to about 350 g/m2 and, more preferably, tv about 250 g/mz.
zo The first absorbent laysrr 46 functions to rapidly absorb and retain fluid which is then more slowly absorbed by the second absorbent layer 48. The first absorbent layer haviryg a r~latively open pore structure readily absorbs and disperses liquid laterally within its bulk and readily transfers tars liquid to th~ receiving surface of the absarbent vote. In tum, the absorbent core having a relatively smaller zs pore structure than the first absorbent layer has good capillarity which efficiently draws liquid into its bulk from the first absarbent layer. Ones the liquid haslbeen absorbed into supc~rabsorbent polymer, the liquid cannot be subsequently released by applying pressure. Therefore, the liquid absorb~3d into the superabsorbent material becomes entrapped. At the same time, the strength with which second 3o absorbent layer intakes liquid from the first absorbent layer helps to reduce the - is -proportion of liquid held in the first absorbent layer, thereby reducing the amount of liquid that returns to the cover layer when the napkin is subjected to rnech~nical loading. Furtlyermore, the first absorbent layer has a relatively high capillarity so that any concentration of liquid in the first at~sorbent l8yer resultin~ from mpchanrcal loading can be redistributed within the material to lower concentrations, again reducing the amount of liquid which can return to the cover layer.
In a specific embodiment, the second absorbsrnt layer 48 contains in the range from about 30 to 40 weight percent superabsorbent material, has a basis io weight in the range from about 200 to 400 q/ri1' and a density in the range from about o_2 to 0.5 g/cc. More speoifically, the density is from about 0.25 g/cc to about 0.45 glc and, even mere spQCifically about 0.3 glee.
Tlae second absorbrrnt layer 48 can be formed as three or four lamina i5 or strata. Those strata include a bottom layer, oar or two middle layers and a top layer. Specific examples of three and four layer material are set forth below.
The SAP can be incWded in any or all of th~ lay~rs. The concentration (weight percent) of 8AP in each layer can vary as can the nature of the particular SAP.
~o Even where prepared as from multiplse layers, the final thickness of the formed second absorbent layer 48 is low. The thickness can vary from less than about 0.5 mm to about 2.5 mm. In a speck ~xample, the thickness is from less than about 0.5 mrtt 1.5 mm.
25 In one embodiment, the cellulosic fiber for use In the second absorbent layer 48 is wood pulp. There ~rc certain characteristics of wood pulp that make It paltlcularly suitable for use. Cellulose in most wood pulps has a crystalline form known as Cellulose I which can be converted to a form known as Cellulose II.
In the second absorbent layer 48, wood pulp with a substantial portion of th~
cellulose as ao Cellulose II could be used. Similarly, pulps having an increased fiber curl value are advaniagevus. Finally, pulps having reduced levels of hemicellulose are preferred.
Means for treating pulps so as to optimize these characteristics are well known in the art. 8y way of example, treating wood pulp with liquid ammonia is known tv convert cellulose to the Cellulose II structure and to increa9e the fiber cur) value.
Flash drying is known to increase the fiber curl valuw of pulp. Cold caustic treatment of pulp decreases hemtcellulose content, increases fiber curl and converts eellutos~
to the Cellulose II form. Thus it could be advantageous that the cellulosic fibers used to produce the material of this invention contrain at least a portion of cold caustic treated PuIP_ ~o Briefly, a caustic treatment is typically carried out at a temperature less than about 80 degree C., but preferably at a temperature less than 50 degree C., and more preferably at a temperature beiwee~~ about 10 degree C. to 40 degree C. A
preferred alkali metal salt solution is a sodium hydroxide solution newly made up or is as a solution by-product in a pulp or pap~r mill operation, e.g., hemiceustic white liquor, oxidized white liquor and the like. Uther alkali metal salts such as ammonium hydroxide and potassium hydroxide and the like can be employed. However, from a cost standpoint, the preferable salt is sodium hydroxide. The concentration of alKall mQtal salts is typically in a rangE from about 2 to about 25 weight percent of the ao solution, and preferably from about 6 to about 18 weight percent. Pulps for high rate, fall absorbing applications are preferably treated with alkali metal salt concentrations from about 10 to'about 18 weight percent.
For further details on the 9tnrcture and the method of construction of 25 the second absorbent layer 48 the read~r is invited to rcfier to the US
patent 5,866,242 granted on February 2, 1999 to Tan et al. Th~ contents of this document are hereby incorporated by reference.
Main Body-Bonier Lavor Underlying the absorbent cyst~m 44 is n berritr layer 50 comprising liquid-impervious 51m material so as to prevent liquid that is entrapped in the absorbent system 44 from egressing the sanitary napkin and staining the wearer's undergarment. Th~ barrier layer 50 is preferably made of polymeric film, although it may be made of liquid-imp~rvious air-permeable material such as repellent-treated, non-woven or mlcroporous films or foams.
The cover layer 42 and the barrier I'yer 50 ar~ joined along their marginal portions so as to form an enclosure or flange seal that forms a unitary i n absorbent product and,maintoins tho absorbent system 44 captive_ The point may be mddo by m~ans of adhRSives, heat-bonding, ultrasonic bonding, radio frequency sealing, rrtechanical crimping, and the like and combinations thereof. The peripheral seal line is shown in Figure 1 by the reference numeral S2.
The flaps 38 and 40 are preferably made as integral extensions of~the coo~r layor 42 and the barrier layer 50. These integral extensions are joined to one anothQr along their marginal seat portions by adhesives, heat-bonding, ultrasonic 2o bonding, radio frequency sealing, mechanical crimping, and the Ilke and combinations thereof. Most preferably, such joining is made at the same time the cover layer 42 and the barrier layer 50 are bonded to ono another to enclose the absorbent system 44. Alternatively, the flaps may include absorbent material between the cover layer and the barrier layer extensions. Such absorbent material may be an extension of the first absorbent layer 46, the second absorbent layer 48 or both.
esiv s Referring to Figures 2 and 3, in order to enhance the stability of the sanitary napkin, the garment facing surtacce of thp barrier layer is provided with an undergarment attachment or positioning adhesive material 58, typically hot-melt adhesive material capable of establishing a temporary bond with the undergarment material. A suitable material is the composition designated HL-1491 XZP
commercially available from H.B. Fuller Canada, Toronto, Ontario, Canada. The positioning adhesive 5E3 may be applied to the garment-facing surtace of the barrier layer 50 in various patterns, including complete adhesive coverage, parallel longitudinal lines, a line of adhesivd following the perimeter of the structure, io transverse lines of adhesive or the like.
Standard release paper 82 (shown only in Figure 3) covers th~
positioning adhesive 58 before the napkin is used to prevent the unwanted adherence of the napkin to itself or foreign objects. The release paper is of ~ conventional construction (e.g. silicone coated wet-laid Kraft wood pulp) and suitable papers are available from Tekkote Corporation (Leonia, New Jersey, USA), and bear th~ designation FRASER 30#/61629.
~iANNEL FpRMATIONS
In a preferred embodiment, the sonitary napkin is provided with et least one and prQferably more than on~ chann~I formation arranged to direct liquid along the channel (or channels) for subsequent absorption into the first absorbent layer-Tne channels are formed by embossing and densifying one yr mere regions of the napkin.
The inventors have found that the provision of channels contributes significantly in reducing the rewet potential. Preferably, the napkin has a plurality of elongate channels formed therein, which are spaced apart from each other and configured to channel IIquId laterally across the body-facing surface of the napkin or near body faring surface portion thereof, away from the region of Initial deposldon.
~v The provision of one or more channels adjacent the coo~r layer enables liquid to be transported rapidly over the napkin so that different regions of the first dbsori~nt layer dc;t effr~clively to dta5urb Um liduiri err Narallc~l. This Irralps lv rnsure thal liquid is presented to a larger portion of the surface area of the second absarbent layer to increase the effectiveness of the second absorbent layer in drawing liquid from the find absorbent layer.
The napkin may be provided wnh a slnflle channel or multiple channels.
for example running along or parallel to the longitudinal axis along the length of the to napkin, obliquely of the longitudinal axis, for example from one side of the napkin to the other or substantially perpendicular to the longitudinal axis. The channels) may have any shape which may be selected according to the particular application, for example the channels may be linear, arcuate or have a serpentine conftpuratlon or a mixture of these as well as other shapes, including a spiral and zig-zag patfierns.
In one embodiment, the napkin has a plurality of discrofis channel formations which are spaced apart and intersect one another_ An example of such an embvdirrrent is shown in Figure 1. Referring to Figure 1, the napkin ZO is provided with a plurality of arcuate channels 10 which extend generally obliquely of the longitudinal 2o centre line 34 from one half of the napkin surface fom~ed by the centre line 34 to the oth~r half. This design efficier>tly conducts liquid simultaneously along the length and across the width of the napkin. I he channel formation may be formed in the cover layer and/or in the first absorbent layer. The channels may be formed advantageously by applying localised pressure to the material as for example is used in embossing.
The vpplied pressure resuHs in densifying the material which defrn~s the floor of the channel rendering it I~ss p~rviouc to liquid and so extending the distance over which the liquid can travel before absorption. The first absorbent (transfer) layer is preferably relatively thick in comparison with the other layers of the napkin which enables relatively deep chanrmls tv be formed. Advantageously, portions of the transfer layer laterally adjacent to the channel remain relatively thick and retains their original, _ 17 ~o relatively open pore structure allowing liquid to he etiiGently drawn from the channel.
A~ivantager~usly, ltm transfc3r layer comprises thermoplastic fibres. The provision of thermoplastic fibr~~ss assists in the formation of a stable antJ perrnanent channel when the thermoplostic fibres and subjected to heat. Whcn heat is applied, the thermoplastic fibres tend to fuse together to farm a more rigid structure so that the original form of the channels is maintained during use and over tune. Conveniently, th~ application of heat may be Incorporated with the embossing process.
Central Absorbent Zone Th~ s~ction of the napkin comprising in vcracal registration the cover, absorbent system and barrier and wherein there is substantially unifiorm composition of absorbent material, Is referred to as the central absorbent zone_ Figures 7a and 7b illustrate an embr~din~nt of a sanitary napkin in which this central absorbent zone 78 !s is depicted_ The stiffness of this zone plays a key role in the performance of the product.
If the central absorbent zone is uniformly too stiff it will not deliver the comfort which is desirable in a thin product. If this zone is unifomnly too flexible it will result in bunching of the product. The central absorbent zone requires that the absorbent sysrE:m include the second absorbent layer 48.
An imporbnt aspoct of the current invention is that one or more rogions of the central absorbent zone will have adequat~ stiffn~ss to avoid extensive bunching.
One or more other regions of the central absorbent zone wilt have a somewhat lower stiffness to insure that the comfiort properties at the prcxiuct are maintained. The 2s napkin is designed to deform in a controlled manner in thex regions. The lower stiffness is obtained in a manner that maintains substantially uniform composition of absorbent materials in the central absorbent zone 76 to thereby maintain good absorbency properdes_ As used herein the terminology "substantially uniform composition of absurk~ent materials" means that the concentration of absorbent so materials is substantially uniform_ Thus, the variations in stiffness within the ventral absorbent zone are not achieved by the addition of or removal of absorbent Of other material but in fact are achieved by a mechanical mod'rflcation of the absorbent material Itself As ~n illustrative example, Figure 7a depicts such a first region 74 of higher stiffs .~ss and a s~cond r~gion 72 of reduced stiffs~ss. As used her~in, th~
terminology 'rwgivn" refers tv an area of at least 12.7 mm by 25.4 mm. In particular, the first region 74 is that area the central absorbent zone which remain unmodified, while the second region 72 is that area in which cuts 70 have been added.
These cuts lr~ are into the second absorbent layer, the first absorbent layer or both.
Figures 7a and 7b also depict an adhesive layer 47 for bonding the first absorbent layer 48 to the second absorbent layer48. As illustrated in Figure 7a, there is a void in the adhesive layer in the second n~gion 72.
i5 Prnferabty the first region (i.e., having higher strffness) of the centre) absorbent zone will have a stiffness greater than 300 grams as m~asur~ed by the peak bending stiffness_ By the Gurley stiffness method (described in detail below) it will have a stiffness measurement greater than about 350 mg. ~ The second region of the central absorbent zone will tyeve siif6iess values of al Isast about 10°!0 less than first rt~ion ao measurement in either of these tesfis.
According to the present invention the main absvrbQnt materials will substantially have un'rtorrn absorbent composition In the central absorbent zone T6 to assure uniform absorbency properties throughout the central absorbent zone.
The Z5 lower stiffness values will be obtained by means other than modified absorbQ6t composition. Seleotivoe use of adhesives between absorbent layers is one such method. That is, those areas where the layers are adhesively bonded will be stiffer than those areas when:: nn adhecive or bonding is pr~sant between layers.

- is -Uther means may be by mechanically rnuriifying either all of the layers in a section of the cxnG~al absorbent zone or any individual material in a section of the central absorbent none. Methods of modification may include adding cuts, slits perforations or tenderizing a~ discussed U.S. Patent Number 4,605,402 to M.
Iskra and U.S. Patient Number 5,466,23? to S. C:adieux et al. These patents are hereby incorporated by reference.
Addiryg selective cuts or perforations is a preferred approach and can b~
done with standard rotating proxss equipment. This approach will typically add cuts to io selective regions of one or both absorbent layen:. The cuts would not typically be added to either the barrier or the cover for obvious fluid containment reasons. The cuts may be individual cuts or they may be multiple cuts in the region of each other to effect the stiffness of the prvduci and provide regions where the product easily deforr»s under body stresses_ The cuts will be more effective if there is no adhesive bonding the i5 sbsorbont layers in the region of the cuts. Flexibility may also be provided by single or multiple cuts or slits or any variety of perfiorating, tenderizing or scoring.
Figures 6-10 each show an alternative embodiment of a sanitary narpkin having a central absorbent zone comprising a centrally loratad, longitudinally extending zo first rogion having a higher stiffness and a second region of reduced siittness adjacent each longitudinal edge of tree central absorbent zone In particular, the fir3t regions 74 are those areas of the central absorbent zone which remain unmodified, while the secorrd regions 72 of decreased stiffness are those in which a plurality of cuts or slits 70 have been added. These cuts aro into the second absorbent layor, th~ first is ebsorbont layer, or both. Each of these figures d~picts an adhesive layer 47,fnr bonding the first absorbent layer 46 to the second ahsorbent layer 48. fps Illustrafied in each of the figures, there is a void In the adhesive layer in the secxmd region of the central absorbent .wne and thus the first and second absortaent layers arE
unafftxed in tt~ srjoond region. Similar voids of a bonding means are present in the reduced stiffness regions of alternative ernk~c~dirnents in which adhesives are not used as the bonding means between layers.
In one embodiment of the present invention, the width of the second io region 7Z, measured in a direction perpendicular to the Iongihrdinal centerline 3d, exceeds 37.5 mm and the length of this region, measured in a din_etion parallel to the Ivngitudinal centerline 34, also exceeds 37.5 mm_ In an alternative embodiment, the corresponding minimum width dimension is 12.7 mm while the length dimension exceeds 2b.4 mm_ Figure 11 Illustrates a prefen~ed embodiment of the invention in which three transverse cuts 70 have been added. F~ch of these cuts is 18.0 mrn wide and each is porpendicular to and bisected by the longitudinal centerline 34. These cuts are perfom~d on th~ second absorbent layer 48 and are complete cuts through the entire i5 thickness of that layer (as Opposed to merely scoring the Iryer). Further, Fi4urp 11 depicts the speGflc positioning of these cuts relative to the longitudinal oerrterline 34 and the imaginary transverse line 36. Still t'urttyer, Figure 11 depicts specific dimensions of the adhesive layer 47 and thereby illustrates the absence of adhesive in the reduced stiffness region 72 in which the cuts are locat~d. As illuctrat~d in the o embodiment of Figure 11 the length of the reduced stiffness region exc~reds 25.4 mm whirs the width exceeds 16.D mm.
Method of monufacture 25 The above-described embodiment of the sanitary napkin 20 is fabricated in a conventional manner in accordance with conventional techniques.
Specffrcally, a laminate structure, sometimes referred to in the art as a web, is created. This laminate structure comprises an expanse of the materials from which the napkin will bo croatod. In other words, the Is~minate structure comprises the 3o following layers of material in a top to-bottom order: an expanse of cover layer material; an expanse of first absorbont layer matorial; an expanse of seoond absorbent layer material (manufactur~d as dQSCribod above); and finally an expanse of barrier layer. Some of the materials are necessarily not continuous within the laminate structure, and where such Is the case, they are poslboned precisely, one with respect to another, in the relationship they will occupy in the final products. The cover layer material and the barrier layer material are then bonded together by applying pressure in the appropriate positions, and what will become th~
peripheral s~al is created. (Tho seal may also be made by means of heat-bonding, ultrasonic bonding, radio frequency sealing, mechanical crimpin8, and the like and ~ o combinations thereof.) The sealed structure is then severed by conventional means (i.e. die-cutting, fluid jet cutting, or by laser) from the web to create a discrete article.
As mentioned above, one or more channels may be formed adjacent the body facing. surface of the napkin, and the channels) may be formed for example by embossing. The channels) may be formed by ether techniques, including cutting, excavating, etching, molding end cauterizing, as well as other methods known to those skilled in the art. If embossing is used, the method may involve passing the sanitary napkin between a pair of rollers, in which one of the rollers includes projections cnnftgured to the desired pmbosslng pattern. The 2o projections cvmprdss and density the rnaleriat loc~rlly dnd may be applied to the cover layer, the absorbent system (particularly, the first absorbent layer) or a combination of the two. The degree of pressure applied during the embossing operation depending upon the type of material and its physical integriiy_ Finding the optimal process conditions in accordance with the spACific application is within the ~s scope of a person skilled in the art. In general, the embossing pressure should be selected to sufficiently density the material locally to form the channels but not fioo high so as to sEVCr the meterial_ As mentioned above, the materiel may also be hQSted and this may b~ don~ conveni~ntly by hosting th~ srmbossing roll~rs.
Ultrasonic embossing may also be used for forming the channel(s).
:~ o Advantageously, embossing helps to hold the various layers of the sanitary napkin together and reduces the likelihood of the cover layer or the battier layer separating from the adjacent layers or coming loos~ when the s~nitary napkin is bent. Preferably, the napkin is embossed at regular intervals over the majority and preferably the entirety of its surface.
The positioning adhesive material is then applied to the banier layer in the appropriate positions, and release papQr i, applied to cover the positioning adhesive. Alternatively, the positioning adhesive, or the positioning adhesive and io the release paper may be applied rn the web before thp individual articles an~_ severed therefrom.
Procedure for Mcas ring the Thickness Qf a Senitarv Arade 15 As indicated earlier, the sanitary napkin 20 has a thickness of about 5 mm or less. The apparatus required to measure the thickness of the sanitary napkin is a footed dial (thickn~ss) gauge, available .from Amos, with a foot having a 1 1/8"
diameter and a stand, 2 0~ deadweight accurate to 0.001". A digital type apparatus fs preferred. If the sanitary napkin sample is individually folded and wrapped. the Zo sample is unwrapped and carefully flattened by hand. The release paper is removed from the sample and it is repositioned back gently across the positioning adhesive lin~s so as not to compress the sample, ensuring that the releas~ patper lies flat across the sample. Flaps (if any) are folded back under the sample, prior t4 taking the thickness reading in the center of the sample.
PPC-?8S

The foot of tfre gauge is raised and the 9emple is placed on the anvil such lhat the foot of the gauge is approximately centred the sample (or in the location of interest on the somple of interest). Whon low~ring the foot, car~
must be taken to prevent th~ foot dropping onto the samp~P or undue force being applied.
After the foot is lowered, the sample and read out are allowed to stabilize for approximately 5 seconds. The thickness reading is then taken.
ce f r urin P ~ pnd- S
to Peak bending stiffness is determined by a test that is modelled after the ASTM D 4032-82 CIRCULAR BEND PROCEDURE, the procedure being considerably modified and performed as follower. The CIRCULAR BEND PROCEDURE is a simultaneous muki-directional dafdrmation of a material in which one face of a specimen becomes concave and the other face beWmes convex. The CIRCULAR
BEND PROCEDURE gives a force value related to flexural resistance, simultaneously averaging stiffness in all directions.
The apparatus necessary for the CIRCULAR BEND PROCEDURE is a modified Circular Bend Stiffness Tester, having the following parts:
1. A smooth-polished steel plate platform which is 102.0 mm by 102.0 by 6.35 mm hflving an 18.75 mm diameter orifice. The lap Rdge of the orhlce should be at a 45 degr~ angle to a depth of 4.75 mm;
3s 2. A plunger having an overall length of 72.2 mm, a diameter of 6.Z5 mm, a ball nosy having a radius of 2.97 mm and a r,ccdlepoint extending 0.88 mm therefrom having a 0.33 mm base diameter and a point having a radius of less than 0.5 mm, the plunger being mounted concentric with the ort~rce end having equal clearance on 911 sides. Note that the needle-point i5 ~rmrely tv prevent lateral r movement of the test specimen during testing_ Therefore, if the needlepoint significantly adversely affects the test specimen (for example, punctures an inflatable structure), than the needlepoint should not be used. The bottom of the plunger should be set well above the top of the orifice plate. From this position, the s downward stroke of the ball nose is to the exact bottom of the plate orifice;
3. A force..measurement gauge and more specifically an Instron inverted compression load eell_ The load cell has a load range of from about 0.0 to about 2000.0 g;
io 4. An actuator and more sp~cifically the Instron Mod~I No. 1122 having an inverted compression load cell. The Instron 1122 is made by the Instron Engineering Corporation. Canton. Mass.
Five representative sanitary napkins ere used for the proccdurE. For ead~ of these napkins one or more sections in th~ centr-di absorbQnt ZenQ era sQlectvd from its second region, where lower stiffness values are expected. 'I~hat is, in these sections cuts or ether modifications have been added. In addition, one or men:
sections in the central absorbent zone are selected from its fiirst region areas wherein 2o no modification.~. have been made and consequently a higher stiffnew value is ~xpvctod. A 37.5 mm by 37.5 mm sampl~ is cut from each of thxa s~I~cted rogionc.
The test specirtrens should not be folded or bent by the test p~rson, and tire handling of specirt~ens must be kept to a minimum and to the edges to avoid 2s affecting flexural-resistance properties. From the four remaining 9enit~ry r!epkins, an equal number "Y" of 37.5 mm by 37_5 mm specimens, identical to the specimens cut from the first napkin, are cut. 't hus, the test person should have "Y" number of sets of free identical specimens.

The procedure for the CIRCULAR BEND PROCEDURE is as follows.
The specimens are conditioned by leaving them in a room that is 21 degree Celsius plus or minus 0.1 degree Gelslus and 509~o plus or minus 2.0~ relative humidity for a period of iwo hours. The test plate is leveled. The plunger speed is set at 50.0 cm s per minute per full stroke length. A specimen is centered on the orifrce platfom~
below the plunger such that the cover layer 42 of the specimen is facing the plunger and the barrier layer 5U of the specimen is facing the platform. The indicator zero is checked and adjusted, if necessary. The plunger is actuated sn that it prpssefi 1hP
specimen in to the orifice until the t~Ullolyl Uf llye bdl) rwse is coplanar with the bvtlom io of the or~ce plate. Touching the specimen during the testing should be avoided. The maximum force reading to the nearest gram is recorded. The about stops are repeated until all fiv! of the identical specimens have been tested.
Th~ peak forve is recorded for each speoimen when it is testied. For each tested rogion on th~ napkins, th~ average of th~ 5 peak forces is calculated and is equal to the peak bending sttffiess for that region of the napkin. For the cases where multiple regions are tested, the maximum of ttm stiffer regions and the lowest of the Zo more flexible regions are taken es representative of the product.
Gur~y Stitfiess Nlaasurorrrent 3tltTness value c;an be measured by either the Peak Bending Stiffne~
Z5 described above or by the Gurley method. As the Gurley method uxs a smaller sample size, it may be more appropriate when the regions of interest is smell~r then the 37.5 mm square sample which is used for the Peak Bending Stiffn~ss Method.
Guriey stiffness is one of many Indices of sttlfiess. Curtsy stiffness 3o measures the bendability or flexibility of absorbent materials. The lovrntr the Guriey stiffness value, the more flexible the material_ The Gurley stiffness values are measured using a Gurley Stiffness Tester (Model No. 4171 E), manufactured by Gudey Precision Instruments of Troy, N.Y. The instrument measures the externally applied moment required to produce a given deflection of a test strip of specific s dimensions fixed at one end and having a concentrated load applied to the other end. The results are obtained in "Gudey Stiffness" values in units of milligrams.
Similar to the PBS method, on~ or more sections in the central absorbent zone are selecfied from its first region, where the highest stiffness values are expected.
~ o As before one or mere sections are also selected from the second region of the central absorbent zone, where lower stiffiess values are expected. These are areas where cuts or other modiflcaflons have been added.
From each chosen section on the five napkins,12.7 by 25.4 mm samples 15 are cut and tested by the standard Gurley stiffness testing proceduros whens a result in milligrams is reported by the tesflng device with the proper input parameters.
Note that the test is performed with one of the 12.7 mm ends of the samples placed in the damp and with the average values taken from deflecfing the sample in both directions.
2o The test samples can be chosen with either the long or short dimensions of the samples in the longer direction of the produck This decision is to be made based on in a manner to maximize the difference between the stiffest and most flexible positions. In the case where cuts are added to the absorb~nt core, the 12.7 mm direction will be parallel by the cuts.
The average values for each region are calculated. For the cases where multjple regions are tested, the maximum of the stiffer regions and the lowest of the more flexible regions are taken as representative of the product.

Applications of the product and mcthvds of the prosent invention for sanitary and other health-care uses can be accomplished by any sanitary protection, incontinence, medical and absorbent methods and techniques as are presently or prospectively known to those skilled in the art. Thus, it is irriended that the present application cover the modii3cativns and variations of this Invention provid~d that they Gome within the scope of the appended claims and their equivalents.

Claims (24)

1. A sanitary napkin adapted to be worn in the crotch portion of an undergarment, said napkin having a thickness of less than about 5 mm and comprising a central absorbent zone; said central absorbent zone comprising a fluid-permeable, body-facing cover layer; a fluid impermeable, garment facing barrier layer, and an absorbent system; said central absorbent zone having substantially uniform composition of absorbent materials and having a width of at least 45 mm;
said central absorbent zone further comprising a first region and a second region adjacent said first region, said first region having a stiffness, and said second region having a stiffness that is less than 90% of the stiffness of the first region.

2. A sanitary napkin as claimed in claim 1, wherein said first region and said second region have a substantially uniform composition of cover layer and barrier layer.

3. A sanitary napkin as claimed in claim 1, wherein said stiffness of the first region is greater than 300 grams as measured by the peak bending stiffness method.

4. A sanitary napkin as claimed in claim 1, wherein said stiffness of the first region is greater than 350 mg as measured by the Gurley stiffness method.

5. A sanitary napkin as Calmed in claim 1, wherein said second region has a stiffness that is less than 80% of the stiffness of the first region.

6. A sanitary napkin as claimed in claim 1, wherein said second region has a stiffness that is less than 60% of the stiffness of the first region.

7. A sanitary napkin as claimed in claim 1, wherein said second region has a stiffness that is less than 50% of the stiffness of the first region.

8. A sanitary napkin as claimed in claim 1 having a thickness of less than about 3.5 mm.

9. A sanitary napkin as claimed in claim 1 having a thickness of less than about 2.8 mm.

10. A sanitary napkin as claimed in claim 1, wherein said absorbent system comprises a first absorbent layer and a second absorbent layer.

11. A sanitary napkin as claimed in claim 10, wherein said first absorbent layer has a basis weight in the range from about 80 to 110 g/m2.

12. A sanitary napkin as claimed in claim 10, wherein said absorbent system further comprises a second absorbent layer.

13. A sanitary napkin as claimed in claim 12, wherein said second absorbent layer has a basis weight in the range from about 100 to 700 g/m2.

14. A sanitary napkin as claimed in claim 13, wherein said second absorbent layer comprises a mixture of cellulosic fibers and superabsorbent materials and wherein said second absorbent layer contains from about 5 weight percent to about 60 weight percent superabsorbent.

15. A sanitary napkin as claimed in claim 12, wherein said first absorbent layer is affixed to said second absorbent layer by an affixation means.

16. A sanitary napkin as claimed in claim 15, wherein said affixation means is adhesive.

17. A sanitary napkin as claimed in claim 15, said second region of the central absorbent zone is substantially free of said affixation means.

18. A sanitary napkin as claimed in claim 12, wherein said second absorbent layer has a thickness from about 0.5 mm to about 2.5 mm

19. A sanitary napkin as claimed in claim 1, wherein said the central absorbent zone has a width of at least 64 mm.

20. A sanitary napkin as claimed in claim 1, wherein said sanitary napkin further comprises a pair of flexible flaps, each flap extending laterally from a longitudinal side of the central absorbent zone.

21. A sanitary napkin as claimed in claim 1, wherein said sanitary napkin further comprises channels.

22. A sanitary napkin as claimed in claim 1, wherein said second region contains one or more mechanical modifications selected from the group consisting of cutting, slitting, perforating or tenderizing.

23. A sanitary napkin as claimed in claim 22, wherein said mechanical modifications comprises a plurality of slits and wherein said second region extends longitudinally adjacent each longitudinal edge of the central absorbent zone.

24. A sanitary napkin as claimed in claim 10, wherein said second region has mechanical modifications comprising a plurality of slits and the first absorbent layer is unaffied to the second absorbent layer in said second region.